Reduced dielectric breakdown/leakage semiconductor device and a method of manufacturing the same, integrated circuit, electro-optical device, and electric apparatus

ABSTRACT

Aspects of the invention provide a method, in a semiconductor device, such as a thin film transistor, a technology capable of preventing or reducing the electric field concentration at the edge section of the semiconductor film to enhance the reliability. The method of manufacturing a semiconductor device according to the invention can include a first step of forming a semiconductor film discretely on an insulation substrate, a second step of covering the semiconductor film including an edge section of the semiconductor film with a first insulation film, a third step of opening the first insulation film above the semiconductor film excluding the edge section of the semiconductor film, a fourth step of forming a second insulation film thinner than the first insulation film on the semiconductor film corresponding to at least the opening of the first insulation film, and a fifth step of forming an electrode wiring film on the second insulation film.

BACKGROUND

Aspects of the invention can relate to an improvement technology of afield-effect semiconductor device, such as a MOS transistor. Researchand development of a technology of forming a thin film transistor havinghigh current drive efficiency using a crystalline semiconductor film(e.g., polycrystalline silicon film) formed by a low-temperature processis in progress. In general, polycrystalline silicon films are formed bycrystallizing amorphous silicon films by irradiating with laser thereto.However, the polycrystalline silicon films thus formed tend to havelarger roughness in surfaces thereof because of protrusions formed ofboundaries (grain boundaries) of crystal grains grown at variousportions during the crystallization. In a thin film field-effecttransistor (TFT) formed by depositing a gate insulation film and a gateelectrode on the upper side of the polycrystalline silicon film,electric field is apt to be concentrated to the protrusions of thesurface of the polycrystalline silicon film to cause dielectricbreakdown of the gate insulation film. In view of such a problem,Japanese Patent Publication No. 2000-40828, for example, discloses atechnology for preventing the dielectric breakdown of the gateinsulation film in the thin film transistor by grinding to planarize thesurface of the formed polycrystalline silicon film.

Incidentally, if the thickness of the gate insulation film is madethinner in order to enhance miniaturization of thin film transistors,the gate insulation film is apt to have a thinner part in the edge ofthe semiconductor film. In particular, when the gate insulation film isformed using a film deposition method having the low step-coveragecapability, such as a sputtering process or a CVD process, the tendencyof the above becomes marked. If the gate electrode is formed so as totraverse the edge portion, the electric field concentration occurs atthat portion to cause the dielectric breakdown very often. Thus,inconvenience of degrading the reliability of the thin film transistorcan occur. In the related art technology described above, it isdifficult to achieve relaxation of such electric field concentration atthe edge portion of the semiconductor film, and therefore, a furtherimproved technology has been desired.

SUMMARY

Aspects of the invention can enhance reliability of semiconductordevices by preventing or reducing the dielectric breakdown or leakagefrom occurring at the edge portion of the semiconductor film in thesemiconductor devices such as thin film transistors.

In order for obtaining the above advantage, an exemplary method ofmanufacturing a semiconductor device can include a first step of forminga semiconductor film discretely on an insulation substrate, a secondstep of covering the semiconductor film including an edge section of thesemiconductor film with a first insulation film, a third step of openingthe first insulation film above the semiconductor film excluding theedge section of the semiconductor film, a fourth step of forming asecond insulation film thinner than the first insulation film on thesemiconductor film corresponding to at least the opening of the firstinsulation film, and a fifth step of forming an electrode wiring film onthe second insulation film. By manufacturing the semiconductor devicewith such manufacturing processes, portions at which the electric fieldis concentrated can be removed from the gate insulation film, thusenhancement of reliability of the gate insulation film can be achieved.

Preferably, the first step can further include the steps of forming thesemiconductor film on the insulation substrate, polycrystallizing thesemiconductor film by a heat treatment, planarizing a surface of thepolycrystallized semiconductor film, and patterning the polycrystallizedsemiconductor film to form an element forming region. Thus, thepolycrystalline semiconductor film with a flat surface can be obtainedto prevent portions, at which the electric field is concentrated, in thegate insulation film from appearing due to the irregularity of thesurface of the semiconductor film.

Preferably, the fourth step described above is the step of forming thesecond insulation film by thermal oxidation of the upper surface of thesemiconductor film. Thus, the gate insulation film thin and superior ininsulation property can be obtained.

Further, the fourth step described above is the step of forming thesecond insulation film by depositing (film-forming) an insulationmaterial on the semiconductor film. Thus, the gate insulation film canbe formed on the semiconductor film without reducing the thickness ofthe semiconductor film.

Further, the exemplary semiconductor device according to the inventioncan be equipped with a semiconductor film formed discretely on aninsulation substrate, an area separating and insulating film formed onthe insulation substrate so as to have an opening on the semiconductorfilm and to surround the periphery of the semiconductor film includingan edge section thereof, a gate insulation film formed thinner than thearea separating and insulating film on the upper surface of thesemiconductor film corresponding to at least the opening of the areaseparating and insulating film, and a gate electrode formed on the gateinsulation film. By adopting such a configuration, portions at which theelectric field is concentrated can be removed from the gate insulationfilm, thus the semiconductor device with enhanced reliability of thegate insulation film can be achieved.

Preferably, the gate insulation film can be formed on the upper surfaceof the semiconductor film displaced from the edge section of thesemiconductor film. Thus, the portions with intense electric field canbe prevented or reduced from appearing in the gate insulation film.

Preferably, the area separating and insulating film can be formed tohave a thickness at least more than twice of that of the gate insulationfilm. Thus, a sufficient insulation property can be ensured to the areaseparating and insulating film.

Further, the integrated circuit, the electro-optic device, or theelectronic apparatus according to the invention is equipped with thesemiconductor device having the configuration described above.

According to the invention, since the gate insulation film is formedaround the edge section of the semiconductor film, the breakdown of thegate insulation film caused by the local electric field concentrationcan be prevented or reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described with reference to the accompanyingdrawings, wherein like numerals reference like elements, and wherein:

FIG. 1 is a plan view for explaining a structure of a thin filmtransistor of a exemplary embodiment;

FIG. 2 is a cross-sectional view of the thin film transistor shown inFIG. 1 along the II-II direction (a channel width direction) in the samedrawing;

FIGS. 3A through 3G are views for explaining a manufacturing method of athin film transistor;

FIGS. 4A through 4G are views for explaining another manufacturingmethod of a thin film transistor;

FIG. 5 is a circuit diagram of a electro-optic device composed of thesemiconductor device; and

FIGS. 6A through 6D are views for explaining illustrative embodiments ofthe electronic apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be described.

FIG. 1 is a plan view for explaining the structure of a thin filmtransistor as a semiconductor device of the exemplary embodimentaccording to the invention. FIG. 2 is a cross-sectional view of the thinfilm transistor along the II-II line direction in the drawing of thethin film transistor shown in FIG. 1. In both of the drawings, thecorresponding sections are denoted with the same reference numerals. Thethin film transistor is used as, for example, a pixel driver element foran organic EL display device, a liquid crystal display device and so on.

As shown in FIGS. 1 and 2, the thin film transistor 1 is a field-effecttransistor having a laminated structure (MOS structure) formed bystacking a semiconductor film, an insulation film, and an electrode, andcomposed of an insulation substrate having an insulation film 11 formedon a substrate 10, semiconductor films 12 formed discretely, aninsulation film (first insulation film) 13 for separating thesemiconductor films, a gate insulation film (second insulation film) 14,a gate electrode 18, a source electrode 20, a drain electrode 22, and aninsulation film (protection film) 24.

The substrate 10 is a substrate made of, for example, glass, quartzglass, or plastic. The insulation film 11 is a primer insulation film,such as a silicon oxide film or silicon nitride film. The insulationfilm 11 electrically insulates the semiconductor films 12 and preventsor reduces impurities from entering from the substrate 10 into thesemiconductor films 12.

The semiconductor film 12 assumes an active region of the thin filmtransistor and is made of a crystalline semiconductor film. In theexemplary embodiment, a polycrystalline silicon film (polysilicon film)can be used as the semiconductor film 12.

The insulation film 13 surrounds the periphery of the discretesemiconductor films 12 formed discretely on the substrate 10, andinsulates the semiconductor films 12 from other semiconductor films notshown to separate the element regions. Further, the insulation film 13is formed so as to cover an edge section 12 a of the semiconductor film12 to expose (open) the upper surface of the edge section 12 a. Theinsulation film 13 is formed to have substantially the same thickness asthe semiconductor film 13. As the insulation film 13, for example, asilicon oxide (SiO₂) film, a silicon nitride (Si₃N₄) film, or phosphorussilicate glass (PSG) film can be preferably used. The insulation film 13needs to be formed as a relatively thick film, but is not required tohave characteristics of an insulation voltage and a fixed charge densityas required to the gate insulation film 14. Therefore, it can be formedwith production conditions suitable for high-speed film deposition.

The gate insulation film 14 is formed so as to cover the upper surfaceof the semiconductor films 12 exposed from the opening sections of theinsulation film 13. In this embodiment, an insulation film made ofsilicon oxide is formed by oxidizing the exposed semiconductor film 12under a plasma atmosphere to obtain the gate insulation film 14. As thegate insulation film 16, for example, a silicon nitride (Si₃N₄) film orthe like can be formed. The gate insulation film 16 has little necessityof formed as a thick film, but is required to have superiorcharacteristics of an insulation voltage, a fixed charge density, and soon. Therefore, it is formed adopting production conditions (generallyfor low-speed film deposition) capable of obtaining better filmcharacteristics. As described below, the gate insulation film 14 can beformed using a deposition process, such as CVD.

The gate insulation film 14, which is separated from the edge section 12a of the semiconductor film 12, becomes difficult to be effected by thelocal high electric field generated adjacent to the edge section 12 a,thus the dielectric breakdown can be prevented.

The gate electrode 18 is formed so as to pass above the insulation film13 and the gate insulation film 14, and also above a predeterminedposition of the semiconductor film 12. In further detail, the gateelectrode 18 is formed so as to traverse two parallel sides of thesemiconductor film 12 as shown in FIG. 1. The gate electrode 18 is madeof an electrically conductive film such as, for example, tantalum,chromium, or aluminum.

Both of the source electrode 20 and the drain electrode 22 respectivelypass through the insulation film 24 to be connected to the semiconductorfilm 12. These source electrodes 20 are composed of electricallyconductive films made of, for example, aluminum.

The insulation film 24 is formed so as to cover the upper surface of thegate electrode 18, the insulation film 16, and so on. The insulationfilm 24 assumes as a protective film, and a silicon oxide (SiO₂) film, asilicon nitride (Si₃N₄) film, phosphorus silicate glass (PSG) film, orthe like is preferably used therefor.

Hereinafter, a manufacturing method of the semiconductor devicedescribed above will be explained with reference to process charts shownin FIGS. 3A through 3G

Firstly, as shown in FIG. 3A, the insulation film 11 made of siliconoxide (SiO₂) is formed on the glass substrate 10 by, for example, aplasma CVD process.

Then, an amorphous silicon film is deposited as the semiconductor film12 thereon by a film forming process such as a PECVD process, a LPCVDprocess, an atmospheric pressure chemical vapor deposition process(APCVD process), or a sputtering process. By executing a process ofirradiating the amorphous silicon film with excimer laser or the like (alaser annealing process), the amorphous silicon film is transformed to apolysilicon film. In this case, on the surface of the polysilicon filmobtained by the crystallization process by the laser irradiation, thereis often provided irregularity 30 caused by protrusions of theboundaries of respective crystal grains (grain boundaries).

Therefore, it is preferable that the semiconductor film 12 is ground tohave the irregularity of the surface thereof be planarized. In thepresent, the processes are executed adopting a CMP process (chemicalmechanical polishing process). As preferable conditions for polishing bythe CMP process, for example, a pad made of soft polyurethane andabrasive (slurry) obtained by dispersing silica particles in ammoniabased or amine based alkaline solution are used in combination adoptingthe conditions of 30000 Pa of pressure, 50 rpm of rotational speed, and200 sccm of flow rate.

Subsequently, as shown in FIG. 3B, the discrete semiconductor film 12composed of the polysilicon film can be formed in the predeterminedelement forming region on the substrate 10 by executing on theplanarized semiconductor film 12 a pattern forming process (patterning)including a photoresist deposition process, a pattern exposing process,a development process, an etching process, and so on.

As shown in FIG. 3C, the insulation film 13 for separating elements canbe formed on the insulation film 11 and the semiconductor film 12. Theinsulation film 13 can be obtained by forming, for example, a siliconoxide (SiO₂) film, a silicon nitride (Si₃N₄) film, or phosphorussilicate glass (PSG) film by the PECVD process. The insulation film 13is formed so as to be thicker enough at the edge section of thesemiconductor film 12 than the gate insulation film 14 in the processdescribed below. For example, it is formed to have the film thicknessmore than double of the thickness of the gate insulation film 14.

As shown in FIG. 3D, a patterning is provided on the insulation film toopen the upper surface of the semiconductor film 12 except the edgesection thereof.

As shown in FIG. 3E, a second insulation film 14 is formed on thesemiconductor film 12 exposed from the opening of the insulation film13. The insulation film 14, which is used as the gate insulation film,needs to be thin and of high withstand voltage. The insulation film 14can be obtained by, for example, thermal-oxidizing the surface of thepolysilicon film, which is the semiconductor film 12, under the plasmaatmosphere including oxygen. Thus, the gate insulation film 14 thinnerthan the insulation film 13 can be formed on the semiconductor film 12corresponding to the opening section. Since the gate insulation film 14is displaced form the edge section 12 a of the semiconductor film 12 andis not formed on the edge section, the problem of decrease of the filmthickness due to the coverage (coverage of the step sections) of theinsulation film 14 does not occur.

As shown in FIG. 3F, the gate electrode and a wiring film 18 are formedin a predetermined position on the gate insulation film 14 by forming ametal film made of tantalum, aluminum, or the like on the insulationfilm 13 and the gate insulation film 14 and then patterning the metalfilm.

Subsequently, using the gate electrode 18 as a mask, impurity ions to bedonors or acceptors are implanted into the semiconductor film 12. Thus,the channel forming region is formed under the gate electrode 18, andthe source/drain region is formed in the other section (ion-implantedsection). A heat treatment is further executed to activate the impurityelements.

As shown in FIG. 3G, the insulation film 24 is formed on the gateelectrode film 18 and the insulation film 13 as a protective film. Asthe insulation film 24, for example, a silicon oxide film of about 500nm thick is formed using the PECVD process.

Further, contacting holes 20, 22 passing through the insulation film 24to reach the source/drain regions are formed. The contacting holes 20and 22 are formed by forming a mask on the insulation film 24 foropening the contacting hole sections and then executing anisotropicetching on the insulation film 24. Further, by depositing aluminuminside the contacting holes and on the insulation film 24 using asputtering process and then puttering it, the source electrode 20, thedrain electrode 22, and the connection wiring are formed.

As described above, in the exemplary embodiment of the invention, sincethe gate insulation film is arranged not to be formed on the edgesection of the semiconductor film or the step section, the portion wherethe electric field is concentrated does not appear in the gateinsulation film, thus enhancing reliability of the gate insulation film.Further, since the gate insulation film is not configured to cover thestep section, film forming or deposition processes having poorefficiency of step coverage can be used for forming the gate insulationfilm.

Another exemplary embodiment of the manufacturing method of thesemiconductor device according to the invention will now be describedwith reference to FIGS. 4A through 4G. In the drawings, correspondingsections to those shown in FIG. 3 are denoted with the same referencenumerals, and the description therefor will be omitted.

In this exemplary embodiment, the gate insulation film 14 is formedusing a deposition process. Also in the embodiment, as shown in FIGS. 4Athrough 4D, the process for forming the semiconductor film 12 on thesubstrate 10 through the process for opening the insulation film 13 arefirstly executed. These processes are the same as the processes(formation of the semiconductor film through formation of the secondinsulation film) shown in FIGS. 3A through 3D described above, andaccordingly the descriptions therefor are omitted.

Subsequently, as shown in FIG. 4E, the second insulation film 14 isformed on the insulation film 13 and the semiconductor film 12 exposedfrom the opening of the insulation film 13. The insulation film 14,which is used as the gate insulation film, needs to be thin and of highwithstand voltage. The insulation film 14 forms a gate insulation film14 made of a silicon oxide film using a deposition process such as aPECVD process. For example, the silicon oxide film is formed usingtetraethoxisilane (TEOS) and oxygen (O₂) as material gases and underconditions of the flow rates of the gases of 50 sccm and 5 slm,respectively, the atmospheric temperature of 350° C., the RF power of1.3 kW, and the pressure of 200 Pa. In this case, the film forming ratebecomes 30 nm/min, and the excellent silicon oxide film provided withthe suitable withstand voltage characteristic for the gate insulationfilm can be obtained.

Thus, the gate insulation film 14 thinner than the insulation film 13can be formed on the semiconductor film 12 corresponding to the openingsection. Since the gate insulation film 14 is displaced form the edgesection 12 a of the semiconductor film 12 and is not formed on the edgesection, the problem of decrease of the film thickness due to thecoverage (coverage of the step sections) of the insulation film 14 doesnot occur.

Subsequently, as shown in FIGS. 4F and 4G, formation of the electrodefilm, formation of the source/drain region, formation of the protectivefilm, and formation of the source/drain electrode wirings are executedthrough the same processes as shown in FIGS. 3F and 3G described aboveto complete the thin film semiconductor.

As described above, in the second embodiment of the manufacturing methodaccording to the invention, since the gate insulation film is arrangednot to be formed on the edge section 12 a of the semiconductor film, theportion where the electric field is concentrated does not appear in thegate insulation film, thus enhancing reliability of the gate insulationfilm. Further, since the gate insulation film is not configured to coverthe edge of the semiconductor film, film forming or deposition processeshaving poor efficiency of step coverage can be used for forming the gateinsulation film.

Hereinafter, some illustrative embodiments of an integrated circuit, anelectro-optic device, and an electronic apparatus composed of thesemiconductor device described above are now described.

FIG. 5 is a circuit diagram of the electro-optic device 100 composed ofthe semiconductor device. The electro-optic device (display device) 100according to the exemplary embodiment is equipped for each of pixelregions with a light emitting layer OELD capable of emitting light withan electroluminescence effect and the holding capacitance for storingthe value of the current for driving the layer, and further equippedwith the semiconductor devices (the thin film transistors T1 through T4)according to the invention. Scanning lines Vsel and light emissioncontrol lines Vgp are supplied from the driver 101 to the respectivepixel areas. From the driver 102, there are supplied data lines Idataand power supply lines Vdd to the respective pixel areas. By controllingthe scanning lines Vsel and the data lines Idata, the currentprogramming to each of the pixel areas is executed, thus the lightemission by the light emission section OELD can be controlled.

Note that the driving circuit described above is one example of acircuit for using the electroluminescent elements as the light emittingelements, and other circuit configurations can also be adopted. Further,the integrated circuit forming each of the drivers 101, 102 is alsopreferably formed using the semiconductor device according to theinvention.

FIGS. 6A through 6D are views for explaining some illustrativeembodiments of electronic apparatus composed of the electro-optic devicedescribed above. FIG. 6A shows an application example to a cellularphone, in which the cellular phone 530 is equipped with an antennasection 531, an audio output section 532, an audio input section 533, anoperating section 534, and the electro-optic device 100 of theinvention. As described above, the electro-optic device according to theinvention can be utilized as a display section.

FIG. 6B shows an application example to a video camera, in which thevideo camera 540 is equipped with a receiver section 541, an operatingsection 542, an audio input section 543, and the electro-optic device100 of the invention.

FIG. 6C shows an application example to a television, in which thetelevision 550 is equipped with the electro-optic device 100 of theinvention. Note that the electro-optic device according to the inventioncan also be adopted to the monitors used for personal computers or thelike.

FIG. 6D shows an application example to a roll-up television, in whichthe roll-up television 560 is equipped with the electro-optic device 100of the invention.

Further, the electronic apparatus is not limited to these examples, butvarious electronic apparatuses having a display function can apply theinvention. For example, other than the above, a facsimile machine havinga display function, a viewfinder of a digital camera, a portable TV, anelectronic notepad, an electronic bulletin board, or a display foradvertisement are also included. Note that the semiconductor deviceaccording to the invention, in addition to the cases in which it isincluded in the electronic apparatuses described above as a component ofthe electro-optic device, can be adopted as an independent component ofthe electronic apparatuses.

Further, it should be understood that the manufacturing method of thesemiconductor device according to the invention is not limited to theabove, but can be applied for manufacturing various kinds of electronicapparatuses. For example, other than the above, it can also be appliedto a facsimile machine having a display function, a viewfinder of adigital camera, a portable TV, a PDA, an electronic notepad, anelectronic bulletin board, a display for advertisement, an IC card, orthe like.

Note that the invention is not limited to the embodiment describedabove, but can be put into practice with various modifications withinthe scope or the spirit of the invention. For example, although thepolysilicon film is cited to explain as an example of the semiconductorfilm in the embodiments described above, the semiconductor film is notlimited thereto, but other semiconductor materials can be used. Further,the semiconductor film (silicon film) or the insulation film (siliconoxide film) can be made using a liquid material, such as a solutionobtained by dissolving polysilazane in an organic solvent.

Further, although the thin film transistor is cited as one example offield-effect semiconductor element in the above exemplary embodiments,the invention can also be applied other than the above in the samemanner to a semiconductor device having a structure in which the elementseparation is realized by etching between respective transistors inmonocrystal SOI (silicon on insulator) transistors.

1. A method of manufacturing a semiconductor device, comprising: forminga semiconductor film discretely on an insulation substrate; forming afirst insulation film on the semiconductor film, the first insulationfilm covering a surface and a side wall of the semiconductor film;providing an opening of the first insulation film to the semiconductorfilm, the opening being smaller than the semiconductor film and within asurface perimeter of the semiconductor film; forming a second insulationfilm that is thinner than the first insulation film on the semiconductorfilm corresponding to the opening of the first insulation film; andforming an electrode wiring film on the second insulation film and apart of the first insulation film.
 2. The method of manufacturing asemiconductor device according to claim 1, forming the semiconductorfilm further including: forming the semiconductor film on the insulationsubstrate; polycrystallizing the semiconductor film by a heat treatment;planarizing a surface of the polycrystallized semiconductor film; andpatterning the polycrystallized semiconductor film to form an elementforming region.
 3. The method of manufacturing a semiconductor deviceaccording to claim 1, forming the second insulating film furtherincluding: forming the second insulation film by thermal oxidation ofthe semiconductor film.
 4. The method of manufacturing a semiconductordevice according to claim 1, forming the second insulating film furtherincluding: forming the second insulation film by depositing aninsulation material on the semiconductor film.